Radar device and method for adjusting among radar sites

ABSTRACT

A radar device includes a generation unit, a transmission unit, and a control unit. The generation unit selectively generates a set of a plurality of transmission signals whose center frequencies are different from one another within an assigned frequency band. The transmission unit emits the transmission signals. The control unit controls the generation unit so as to vary the center frequencies for each emission of the transmission signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of PCT Application No.PCT/JP2006/320110, filed Oct. 6, 2006, which was published under PCTArticle 21(2) in Japanese.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-295459, filed Oct. 7, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radar device and a method foradjusting to remove radio wave interference occurring among radar sites.

2. Description of the Related Art

A radar device (hereinafter, referred to as interfered station)sometimes receives a radio wave (hereinafter, referred to astransmission signal) emitted from other adjacent radar devices(hereinafter, referred to as interfering station), or a radio wave(hereinafter, referred to as echo signal) emitted from the interferingstation and reflected from a target. If a center frequency of thereceived signal is close to a center frequency of a transmitted signal,interference occurs. Therefore, a conventional radar device has aninterference wave removal function (“Revised Radar Technique” Supervisedby Takashi Yoshida, Published by The Institute of Electronics,Information and Communication Engineers, Page 217). As an example of theinterference wave removal function, there is a method for mutuallyamplitude-comparing echo signals at a prescribed distance in acontinuous pulse repetition interval (PRI), assuming that an echo signalwith a large amplitude difference as an interference wave, and replacingthe echo signal with an amplitude value of the echo signal received inthe last PRI.

However, in practice, if pulse repetition frequencies (PRFs) of theinterfering stations are close to one another, or if the number of theinterfering stations is large, a plurality of interference waves areresulted in continuous receptions and, these interference waves affectthe precision of radar signal processing data.

As a related problem, in a radar device emitting transmission signalshaving a plurality of types of pulse widths and moderation methods,overlapping a secondary echo with a weak real echo signal makes itdifficult the real echo signal.

Further, in a radar device using a plurality of types of transmissionpulse signals, interference among pulse signals significantly affect thedetection precision of the echo signal. For example, in a pulsecompression radar device using a short pulse and a long pulse in thePRF, the short pulse for short range leaks into a long-range area, andit results in reducing the echo detection precision of the long pulse.

As mentioned above, in the conventional radar device, if pulserepetition frequencies (PRFs) of the interfering stations are close toone another, or if the number of the interfering stations is large,these interference waves affect on the precision of the radar signalprocessing data. Increasing the effect of the secondary echo reduces thedetection precision of the real echo signal. Further, in the case ofusing a plurality of types of transmission pulse signals, theinterference among the pulse signals significantly affect the detectionprecision of the echo signal.

BRIEF SUMMARY OF THE INVENTION

A radar device regarding the invention includes a generation unit whichselectively generates a set of a plurality of transmission signals whosecenter frequencies are different from one another within an assignedfrequency band, a transmission unit which emits the transmissionsignals, and a control unit which controls the generation unit so as tovary the center frequencies for each emission of the transmissionsignals.

A radar device regarding the invention includes a generation unit whichselectively generates transmission signals in a plurality of types ofpulse widths or modulation methods, a transmission unit which emits thetransmission signals, and a control unit which varies the types of pulsewidths or modulation methods for each emission of the transmissionsignals.

A method for adjusting among radar sites, each radar site performsgenerating selectively a set of a plurality of transmission signalsdiffering from one another in center frequency, emitting thetransmission signals, switching the center frequencies of thetransmission signals for each emission of the transmission signals, andassociating with one or more other radar sites for controlling theswitching so that each of the center frequencies of the each radar sitesdo not overlap with a center frequency of a transmission signal of theone or more other radar site.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram illustrating an example of a configuration ofa radar device regarding one embodiment of the invention;

FIG. 2 is a timing diagram illustrating an example in the case in whichinterference waves get mixed in with and overlap the waves generated bya radar device of a conventional method;

FIG. 3 is a timing diagram illustrating an example in the case in whichit is assumed that the invention is applied to a station sufferinginterference (an interfered station) to vary the center frequencies foreach transmission, a PRF and a signal waveform of an interfering stationare the same as those of the interfered station and also centerfrequencies for each transmission are constant; and

FIG. 4 is a timing diagram illustrating an example in the case in whichthe invention is applied to both an interfered station and interferingstation to vary the center frequencies for each transmission.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be described indetail with reference to the drawings.

FIG. 1 is a block diagram showing an example of a configuration of aradar device regarding one embodiment of the invention. In FIG. 1, atiming control unit 11 controls processing of the whole of the device,and mainly controls the processing timings of a transmission sort signalgeneration unit 12, a frequency control unit 13 and a reception signalprocessing unit 14.

The generation unit 12 generates a transmission sort signal of a presetRPF, pulse width and modulation method in accordance with an instructionfrom the timing control unit 11. The frequency control unit 13 controlsan oscillation frequency from a local oscillator 15 and a passingfrequency band of a first band pass filter 17, and the reception signalprocessing unit 14 performs processing to detect a target from areceived echo signal.

By drive control performed by the timing control unit 11, thetransmission sort signal generated from the signal generation unit 12 ismixed with a local signal output from the oscillator 15 at a first mixer16 to be converted into a signal in a radio frequency (RF) band. Thefirst band pass filter 17 removes a signal of a video frequencycomponent from the transmission sort signal in the RF band; thereby itextracts only a signal of a desired frequency component. The signalextracted here is amplified by a first amplifier 18 to be a transmissionsignal, supplied to an antenna unit 20 through a circulator 19, andemitted to the atmosphere via the antenna unit 20.

The echo signal generated through the emission of the transmissionsignal to the atmosphere and through the reflection at the object iscaught by an antenna unit 20 and supplied to a second amplifier 21 viathe circulator 19. The echo signal supplied to the second amplifier 21is amplified by the second amplifier 21 and frequency-converted into asignal in an intermediate frequency (IF) band together with the signaltransmitted from the local oscillator 15. Then, a second band passfilter 23 removes the signal of the video frequency component, theinterference waves differing in the center frequency and an unnecessarysignal such as a secondary echo, and extracts only the signal of thedesired frequency component. The signal extracted here is supplied tothe reception signal processing unit 14 for processing, such as that forinterference removal.

The feature of the embodiment is to have a function of varying thetransmission frequencies of the transmission signals emitted to theatmosphere by switching the oscillation frequency of the localoscillator 15 and the frequency property of the first band pass filter17 by means of the frequency control unit 13 for each emission of thetransmission signals.

In the aforementioned configuration, operations of the invention will bedescribed with reference to FIG. 2, FIG. 3 and FIG. 4 hereinafter.

FIG. 2 shows an example in the case in which interference waves getmixed in and overlap with the waves of a radar device in a conventionalmethod, and it is presumed that RPFs, signal waveforms and centerfrequencies of the interference waves are the same as those of thetransmission signal transmitted from the interfered station. In thiscase, the level of the echo signal which has passed through theinterference removal function and has been detected as larger than thatof the real echo signal, so there is a possibility that the conventionalradar device conducts erroneous detection.

FIG. 3 shows an example of the case in which it is supposed that theinvention is applied to the interfered station to vary the centerfrequencies of the transmission signals in order of f1, f2, f3 and f4 atevery transmission, the PRFs and the signal waveforms of theinterference waves from the interfering stations are the same as thoseof the transmission signal from the interfered station, and also thecenter frequency for each transmission is f3 and constant. In this case,except for the case where the center frequency of the interfered stationis f3, the interfering waves are removed from the echo signal in passingthrough the second band pass filter 23.

When the center frequency is f3, the signal level becoming larger thanthose of the signals with other center frequencies, the conventionalinterference wave removal function can remove the interference waves;thereby the real echo signal can be detected.

FIG. 4 shows an example of the case in which the present invention isapplied to the interfered station to vary the center frequencies inorder of f1, f2, f3 and f4 for each transmission, and further, theinvention is applied to the interfering station to vary the centerfrequencies in order of f4, f3, f2 and f1 for each transmission so asnot to overlap with one another in a different timing from that of theinterfered station. Like this, by applying the invention to both theinterfered station and interfering station, all interference waves areremoved when they pass through the second band pass filter 23.

Replacing the interference waves in FIG. 2, FIG. 3 and FIG. 4 with thesecondary echo shows that the invention is also effective in removingthe secondary echo.

Therefore, the radar device having the foregoing configuration reducesthe effects of the interference waves and secondary echo by using aplurality of frequencies within the assigned frequency bands and byvarying the center frequencies of the transmission signals to be emittedfor each transmission. Accordingly, even if the PRFs of the interferingstations are close to one another or the number of the interferingstations is large, the radar device can reduce the effects on thereceived and processed data caused by the interference waves, and canreduce the effects of the secondary echo to improve the detectionprecision of the real echo signal to this reduction.

The invention of the aforementioned embodiment having varied theoscillation frequency of the local oscillator 15 and the frequencyproperty of the first band pass filter 17 by the frequency control unit13 for each transmission and having enabled the transmission frequencyof the transmission signal emitted to the atmosphere to be varied, isnot limited to this, and is also achievable in the case in which thefrequency of the transmission sort signal transmitted from thetransmission sort signal generation unit 12, the frequency of the signalprocessed by the reception signal processing unit 14, and the frequencyproperties of the first and second band pass filters 17 and 23 arevaried, in the case in which only the oscillation frequency from thelocal oscillator 15 is varied, or in the case in which the frequency ofthe transmission sort signal transmitted from the transmission sortsignal generation unit 12 and the frequency of the signal processed bythe reception signal processing unit 14 are varied. The types of thetransmission sort signal are achievable by adopting an unmodulated pulsesignal and an amplitude or frequency-modulated pulse signal, and theinvention is applicable to a transmitting/receiving system in a doublesuper heterodyne method. The function of extracting only the signal withthe desired frequency component by removing the interference wavesdifferent in center frequency and the unnecessary signal such as asecondary echo, in the second band pass filter 23 can be also berealized via digital processing, such as by Fourier transformprocessing.

When the invention is applied to all the radar devices of the radarsites in the same assigned frequency band, by switch-controllingfrequencies of the transmission signals so that the waves of the radarsites do not associate to overlap with one another, mutual interferenceis avoided. In the future, it is expected that the assigned frequencybands will be further narrowed, and thus this invention is veryeffective from the point of view of making effective use of frequencybands.

In addition, the invention is not limited to the specific details andrepresentative embodiments shown and described herein, and in animplementation phase, this invention may be embodied in various formswithout departing from the sprit or scope of the general inventiveconcept thereof. Various modifications of the invention can be made byappropriately combining a plurality of constituent elements disclosed inthe foregoing embodiments. Some of the constituent elements, forexample, may be omitted from the whole of the constituent elements shownin the embodiments. Further. The constituent elements over differentembodiments may be appropriately combined.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

The present invention is usable for all types of primary radar device,such as an airport surveillance radar (ASR), a precision approach radar(PAR), and a weather radar (W/R).

1. A radar device comprising: a generation unit which selectively generates a set of a plurality of transmission signals whose center frequencies are different from one another within an assigned frequency band; a transmission unit which emits the transmission signals; and a control unit which controls the generation unit so as to vary the center frequencies for each emission of the transmission signals.
 2. A radar device comprising: a generation unit which selectively generates transmission signals in a plurality of types of pulse widths or modulation methods; a transmission unit which emits the transmission signals; and a control unit which varies the types of pulse widths or modulation methods for each emission of the transmission signals.
 3. The radar device according to claim 1, further comprising an unnecessary wave removing unit which activates the control unit and removes a frequency component of a second transmission signal emitted from an interfering station or a frequency component of an echo signal emitted from the interfering station and reflected from an object, from each of reception signals corresponding to the transmission signals, a center frequency of the second transmission signal or the echo signal being close to the center frequency of each of the transmission signals.
 4. The radar device according to claim 2, further comprising a secondary echo removing unit which activates the control unit to remove a secondary echo signal in a different type of pulse widths or modulation methods or in a different timing from the transmission signals.
 5. A method for adjusting among radar sites, each radar site performing: generating selectively a set of a plurality of transmission signals differing from one another in center frequency; emitting the transmission signals; switching the center frequencies of the transmission signals for each emission of the transmission signals; and associating with one or more other radar sites for controlling the switching so that each of the center frequencies of the each radar sites do not overlap with a center frequency of a transmission signal of the one or more other radar sites.
 6. The method for adjusting among the radar sites according to claim 5, wherein each of the radar sites removes a frequency component of a second transmission signal emitted from interfering radar sites or a frequency component of an echo signal emitted from the interfering radar sites and reflected from an object, from each of reception signals corresponding to the transmission signals, a center frequency of the second transmission signal or the echo signal being close to the center frequency of each of the transmission signals.
 7. The method for adjusting among radar sites according to claim 5, wherein each of the radar sites removes secondary echo signals other than the types or timing of the transmission signals. 